The invention relates to a fully jacketed helical centrifuge for the separation of a mixture of solids and liquids, having an at least partially conical drum which can be driven in rotation, and a conveyor helix which can be driven for rotation within the drum at a differential rotatory speed, whose spirals are adapted in shape to the internal wall of the drum and convey the solid matter settling in the separating chamber formed between the nave of the helix and the drum to a solids outlet formed in the conically tapering end portion of the drum, and having a paring system in a chamber which is provided in the drum end portion opposite the solids outlet end for the removal of a first liquid phase, and a discharge chamber for a second liquid phase, which is defined in relation to the separating chamber by a weir, closed off from the input chamber, and provided in the end cover of the drum, and at least one separating disk partially immersed in the specifically heavier liquid phase and constructed in the form of a termination of the helix.
A fully jacketed helical centrifuge of this kind is known through GB Pat. No. 1,518,680 and operates as a so-called three-phase decanter in which the specifically heavier liquid phase can be taken out under pressure by a paring system and the specifically lighter liquid phase is discharged without pressure over a weir into a receiving chamber of the centrifuge housing.
However, fully jacketed helical centrifuges are also known which remove the specifically lighter liquid phase under pressure by means of a paring system, and discharge the specifically heavier liquid phase under no pressure.
Fully jacketed helical centrifuges, in which the two liquid phases can be ejected under pressure by means of paring systems, present considerable design difficulties, because the liquids have to be transferred from one revolving centrifugal part into another which revolves at a different speed. Therefore, fully jacketed helical centrifuges are used mostly with a paring system for the removal of one of the liquid phases under pressure, while the second liquid phase is removed without pressure, for example over an adjustable weir.
Fully jacketed helical centrifuges of this kind are used in many ways in the chemical and pharmaceutical industry, and for a great variety of purposes, and often one liquid phase may consist of an aqueous liquid and the other of a solvent such as acetate, benzene, chloroform or the like. Since such solvents are very volatile by nature, they are inclined to evaporate rapidly. In addition, they are often toxic or explosive and cause severe harm to the health of the personnel serving the centrifuges unless appropriate protective measures are taken. For these reasons it is necessary to remove at least the solvent phase from the centrifuge under pressure and not to let it leave the centrifuge at atmospheric pressure, which would always involve increased evaporation.
Since on the other hand such solvents may be either lighter or heavier in specific gravity than the aqueous phase, different centrifuge designs must be used, or, in the event of a product changeover, a considerable replacement of parts of the centrifuge is necessary if the solvent phase is in all cases to be removed under pressure. This is especially true when such centrifuges are used in washing or extraction processes.